1 files changed, 132 insertions, 53 deletions

diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
index 64ef09a6cccb..beb91a13a312 100644
--- a/drivers/gpu/drm/drm_modeset_lock.c
+++ b/drivers/gpu/drm/drm_modeset_lock.c
@@ -21,9 +21,13 @@
  * OTHER DEALINGS IN THE SOFTWARE.
  */
 
-#include <drm/drmP.h>
+#include <linux/export.h>
+
+#include <drm/drm_atomic.h>
 #include <drm/drm_crtc.h>
+#include <drm/drm_device.h>
 #include <drm/drm_modeset_lock.h>
+#include <drm/drm_print.h>
 
 /**
  * DOC: kms locking
@@ -35,24 +39,38 @@
  * of extra utility/tracking out of our acquire-ctx.  This is provided
  * by &struct drm_modeset_lock and &struct drm_modeset_acquire_ctx.
  *
- * For basic principles of &ww_mutex, see: Documentation/locking/ww-mutex-design.txt
+ * For basic principles of &ww_mutex, see: Documentation/locking/ww-mutex-design.rst
  *
  * The basic usage pattern is to::
  *
- *     drm_modeset_acquire_init(&ctx)
+ *     drm_modeset_acquire_init(ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
  *     retry:
  *     foreach (lock in random_ordered_set_of_locks) {
- *         ret = drm_modeset_lock(lock, &ctx)
+ *         ret = drm_modeset_lock(lock, ctx)
  *         if (ret == -EDEADLK) {
- *             drm_modeset_backoff(&ctx);
- *             goto retry;
+ *             ret = drm_modeset_backoff(ctx);
+ *             if (!ret)
+ *                 goto retry;
  *         }
+ *         if (ret)
+ *             goto out;
  *     }
  *     ... do stuff ...
- *     drm_modeset_drop_locks(&ctx);
- *     drm_modeset_acquire_fini(&ctx);
+ *     out:
+ *     drm_modeset_drop_locks(ctx);
+ *     drm_modeset_acquire_fini(ctx);
+ *
+ * For convenience this control flow is implemented in
+ * DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END() for the case
+ * where all modeset locks need to be taken through drm_modeset_lock_all_ctx().
+ *
+ * If all that is needed is a single modeset lock, then the &struct
+ * drm_modeset_acquire_ctx is not needed and the locking can be simplified
+ * by passing a NULL instead of ctx in the drm_modeset_lock() call or
+ * calling  drm_modeset_lock_single_interruptible(). To unlock afterwards
+ * call drm_modeset_unlock().
  *
- * On top of of these per-object locks using &ww_mutex there's also an overall
+ * On top of these per-object locks using &ww_mutex there's also an overall
  * &drm_mode_config.mutex, for protecting everything else. Mostly this means
  * probe state of connectors, and preventing hotplug add/removal of connectors.
  *
@@ -62,6 +80,53 @@
 
 static DEFINE_WW_CLASS(crtc_ww_class);
 
+#if IS_ENABLED(CONFIG_DRM_DEBUG_MODESET_LOCK)
+static noinline depot_stack_handle_t __drm_stack_depot_save(void)
+{
+	unsigned long entries[8];
+	unsigned int n;
+
+	n = stack_trace_save(entries, ARRAY_SIZE(entries), 1);
+
+	return stack_depot_save(entries, n, GFP_NOWAIT | __GFP_NOWARN);
+}
+
+static void __drm_stack_depot_print(depot_stack_handle_t stack_depot)
+{
+	struct drm_printer p = drm_dbg_printer(NULL, DRM_UT_KMS, "drm_modeset_lock");
+	unsigned long *entries;
+	unsigned int nr_entries;
+	char *buf;
+
+	buf = kmalloc(PAGE_SIZE, GFP_NOWAIT | __GFP_NOWARN);
+	if (!buf)
+		return;
+
+	nr_entries = stack_depot_fetch(stack_depot, &entries);
+	stack_trace_snprint(buf, PAGE_SIZE, entries, nr_entries, 2);
+
+	drm_printf(&p, "attempting to lock a contended lock without backoff:\n%s", buf);
+
+	kfree(buf);
+}
+
+static void __drm_stack_depot_init(void)
+{
+	stack_depot_init();
+}
+#else /* CONFIG_DRM_DEBUG_MODESET_LOCK */
+static depot_stack_handle_t __drm_stack_depot_save(void)
+{
+	return 0;
+}
+static void __drm_stack_depot_print(depot_stack_handle_t stack_depot)
+{
+}
+static void __drm_stack_depot_init(void)
+{
+}
+#endif /* CONFIG_DRM_DEBUG_MODESET_LOCK */
+
 /**
  * drm_modeset_lock_all - take all modeset locks
  * @dev: DRM device
@@ -83,7 +148,7 @@ void drm_modeset_lock_all(struct drm_device *dev)
 	struct drm_modeset_acquire_ctx *ctx;
 	int ret;
 
-	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
 	if (WARN_ON(!ctx))
 		return;
 
@@ -103,6 +168,7 @@ retry:
 		kfree(ctx);
 		return;
 	}
+	ww_acquire_done(&ctx->ww_ctx);
 
 	WARN_ON(config->acquire_ctx);
 
@@ -173,7 +239,11 @@ EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
 /**
  * drm_modeset_acquire_init - initialize acquire context
  * @ctx: the acquire context
- * @flags: for future
+ * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE
+ *
+ * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags,
+ * all calls to drm_modeset_lock() will perform an interruptible
+ * wait.
  */
 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
 		uint32_t flags)
@@ -181,6 +251,9 @@ void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
 	memset(ctx, 0, sizeof(*ctx));
 	ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
 	INIT_LIST_HEAD(&ctx->locked);
+
+	if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
+		ctx->interruptible = true;
 }
 EXPORT_SYMBOL(drm_modeset_acquire_init);
 
@@ -202,7 +275,9 @@ EXPORT_SYMBOL(drm_modeset_acquire_fini);
  */
 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
 {
-	WARN_ON(ctx->contended);
+	if (WARN_ON(ctx->contended))
+		__drm_stack_depot_print(ctx->stack_depot);
+
 	while (!list_empty(&ctx->locked)) {
 		struct drm_modeset_lock *lock;
 
@@ -220,12 +295,13 @@ static inline int modeset_lock(struct drm_modeset_lock *lock,
 {
 	int ret;
 
-	WARN_ON(ctx->contended);
+	if (WARN_ON(ctx->contended))
+		__drm_stack_depot_print(ctx->stack_depot);
 
 	if (ctx->trylock_only) {
 		lockdep_assert_held(&ctx->ww_ctx);
 
-		if (!ww_mutex_trylock(&lock->mutex))
+		if (!ww_mutex_trylock(&lock->mutex, NULL))
 			return -EBUSY;
 		else
 			return 0;
@@ -251,53 +327,41 @@ static inline int modeset_lock(struct drm_modeset_lock *lock,
 		ret = 0;
 	} else if (ret == -EDEADLK) {
 		ctx->contended = lock;
+		ctx->stack_depot = __drm_stack_depot_save();
 	}
 
 	return ret;
 }
 
-static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
-		bool interruptible)
+/**
+ * drm_modeset_backoff - deadlock avoidance backoff
+ * @ctx: the acquire context
+ *
+ * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
+ * you must call this function to drop all currently held locks and
+ * block until the contended lock becomes available.
+ *
+ * This function returns 0 on success, or -ERESTARTSYS if this context
+ * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the
+ * wait has been interrupted.
+ */
+int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
 {
 	struct drm_modeset_lock *contended = ctx->contended;
 
 	ctx->contended = NULL;
+	ctx->stack_depot = 0;
 
 	if (WARN_ON(!contended))
 		return 0;
 
 	drm_modeset_drop_locks(ctx);
 
-	return modeset_lock(contended, ctx, interruptible, true);
-}
-
-/**
- * drm_modeset_backoff - deadlock avoidance backoff
- * @ctx: the acquire context
- *
- * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
- * you must call this function to drop all currently held locks and
- * block until the contended lock becomes available.
- */
-void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
-{
-	modeset_backoff(ctx, false);
+	return modeset_lock(contended, ctx, ctx->interruptible, true);
 }
 EXPORT_SYMBOL(drm_modeset_backoff);
 
 /**
- * drm_modeset_backoff_interruptible - deadlock avoidance backoff
- * @ctx: the acquire context
- *
- * Interruptible version of drm_modeset_backoff()
- */
-int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
-{
-	return modeset_backoff(ctx, true);
-}
-EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
-
-/**
  * drm_modeset_lock_init - initialize lock
  * @lock: lock to init
  */
@@ -305,6 +369,7 @@ void drm_modeset_lock_init(struct drm_modeset_lock *lock)
 {
 	ww_mutex_init(&lock->mutex, &crtc_ww_class);
 	INIT_LIST_HEAD(&lock->head);
+	__drm_stack_depot_init();
 }
 EXPORT_SYMBOL(drm_modeset_lock_init);
 
@@ -313,17 +378,24 @@ EXPORT_SYMBOL(drm_modeset_lock_init);
  * @lock: lock to take
  * @ctx: acquire ctx
  *
- * If ctx is not NULL, then its ww acquire context is used and the
+ * If @ctx is not NULL, then its ww acquire context is used and the
  * lock will be tracked by the context and can be released by calling
  * drm_modeset_drop_locks().  If -EDEADLK is returned, this means a
  * deadlock scenario has been detected and it is an error to attempt
  * to take any more locks without first calling drm_modeset_backoff().
+ *
+ * If the @ctx is not NULL and initialized with
+ * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with
+ * -ERESTARTSYS when interrupted.
+ *
+ * If @ctx is NULL then the function call behaves like a normal,
+ * uninterruptible non-nesting mutex_lock() call.
  */
 int drm_modeset_lock(struct drm_modeset_lock *lock,
 		struct drm_modeset_acquire_ctx *ctx)
 {
 	if (ctx)
-		return modeset_lock(lock, ctx, false, false);
+		return modeset_lock(lock, ctx, ctx->interruptible, false);
 
 	ww_mutex_lock(&lock->mutex, NULL);
 	return 0;
@@ -331,21 +403,19 @@ int drm_modeset_lock(struct drm_modeset_lock *lock,
 EXPORT_SYMBOL(drm_modeset_lock);
 
 /**
- * drm_modeset_lock_interruptible - take modeset lock
+ * drm_modeset_lock_single_interruptible - take a single modeset lock
  * @lock: lock to take
- * @ctx: acquire ctx
  *
- * Interruptible version of drm_modeset_lock()
+ * This function behaves as drm_modeset_lock() with a NULL context,
+ * but performs interruptible waits.
+ *
+ * This function returns 0 on success, or -ERESTARTSYS when interrupted.
  */
-int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
-		struct drm_modeset_acquire_ctx *ctx)
+int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock)
 {
-	if (ctx)
-		return modeset_lock(lock, ctx, true, false);
-
 	return ww_mutex_lock_interruptible(&lock->mutex, NULL);
 }
-EXPORT_SYMBOL(drm_modeset_lock_interruptible);
+EXPORT_SYMBOL(drm_modeset_lock_single_interruptible);
 
 /**
  * drm_modeset_unlock - drop modeset lock
@@ -374,11 +444,14 @@ EXPORT_SYMBOL(drm_modeset_unlock);
  * Locks acquired with this function should be released by calling the
  * drm_modeset_drop_locks() function on @ctx.
  *
+ * See also: DRM_MODESET_LOCK_ALL_BEGIN() and DRM_MODESET_LOCK_ALL_END()
+ *
  * Returns: 0 on success or a negative error-code on failure.
  */
 int drm_modeset_lock_all_ctx(struct drm_device *dev,
 			     struct drm_modeset_acquire_ctx *ctx)
 {
+	struct drm_private_obj *privobj;
 	struct drm_crtc *crtc;
 	struct drm_plane *plane;
 	int ret;
@@ -399,6 +472,12 @@ int drm_modeset_lock_all_ctx(struct drm_device *dev,
 			return ret;
 	}
 
+	drm_for_each_privobj(privobj, dev) {
+		ret = drm_modeset_lock(&privobj->lock, ctx);
+		if (ret)
+			return ret;
+	}
+
 	return 0;
 }
 EXPORT_SYMBOL(drm_modeset_lock_all_ctx);